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首页> 外文期刊>Contributions to Mineralogy and Petrology >Magmatic evolution of the South Shetland Islands, Antarctica, and implications for continental crust formation
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Magmatic evolution of the South Shetland Islands, Antarctica, and implications for continental crust formation

机译：南设得兰群岛的岩浆演化及其对大陆结壳的影响

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Lavas from the South Shetland Islands volcanic arc (northern Antarctic Peninsula) have been investigated in order to determine the age, petrogenesis and compositional evolution of a long-lived volcanic arc constructed on 32-km-thick crust, a thickness comparable with average continental crust. New 40Ar–39Ar ages for the volcanism range between 135 and 47 Ma and, together with published younger ages, confirm a broad geographical trend of decreasing ages for the volcanism from southwest to northeast. The migration pattern breaks down in Palaeogene time, with Eocene magmatism present on both Livingston and King George islands, which may be due to a change in both subduction direction and velocity after c. 60 Ma. The lavas range from tholeiitic to calc-alkaline, but there is no systematic change with age or geographic location. The compositions of lavas from the north-eastern islands indicate magma generation in a depleted mantle wedge with relatively low Sr and high Nd isotopic compositions and low U/Nb, Th/Nd and Ba/Nb ratios that was metasomatized by hydrous fluids from subducted basaltic oceanic crust. Lavas from the south-western islands show an additional sedimentary influence most likely due to fluid release from subducted sediments into the mantle wedge. Although magmatic activity in the South Shetland arc extended over c. 100 m.y., there is no evolution towards more enriched or evolved magmas with time. Few South Shetland arc lavas are sufficiently enriched with incompatible elements to provide a potential protolith for the generation of average continental crust. We conclude that even long-established subduction zones with magmatic systems founded on relatively thick crust do not necessarily form continental crustal building blocks. They probably represent only the juvenile stages of continental crust formation, and additional re-working, for example during subsequent arc-continental margin collision, is required before they can evolve into average continental crust.
机译：为了确定在32公里厚的地壳上建造的长寿命火山弧的年龄，岩石成因和成分演化，已对南设得兰群岛火山弧（南极半岛）的拉瓦斯进行了研究，以确定其年龄，岩石成因和组成演化。 。火山活动的新 40 Ar– 39 Ar年龄介于135至47 Ma之间，再加上已公布的较年轻年龄，证实了从西南到东北。迁移模式在古近纪时期破裂，利文斯顿岛和乔治国王岛均出现始新世岩浆，这可能是由于c之后俯冲方向和速度都发生了变化。 60毫安熔岩的范围从生硬性到钙碱性，但没有随年龄或地理位置的变化而变化。来自东北岛屿的熔岩成分表明，在贫化的地幔楔中形成了岩浆，具有相对较低的Sr和较高的Nd同位素组成以及较低的U / Nb，Th / Nd和Ba / Nb比值，而这些比值是由俯冲的玄武岩中的含水流体交代的大洋地壳。来自西南岛屿的拉瓦斯显示出额外的沉积影响，这很可能是由于俯冲沉积物中的流体释放到地幔楔中。虽然南设得兰群岛的岩浆活动扩展到c。每年100毫米，没有随着时间的推移而向更富集或演化的岩浆演化。南设得兰群岛弧形熔岩中很少含有不相容元素，足以为产生普通大陆壳提供潜在的原生石。我们得出的结论是，即使是建立在较厚地壳上的具有岩浆系统的长期俯冲带也不一定形成大陆地壳构造块。它们可能仅代表大陆壳形成的幼年阶段，例如在随后的弧-大陆边缘碰撞期间，还需要进行额外的重新加工，才能演化为平均大陆壳。

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